Plant and method for making continuous elastic yarns made of silicone material and continuous elastic yarn made of silicone material thus obtained

ABSTRACT

A plant and method for making continuous yarns made of silicone material comprises at least an extrusion station, into which the material is introduced in an amorphous condition, and extrusion means which cause the material to exit from the extrusion station along an extrusion axis. The plant also comprises a vulcanization station, located downstream of the extrusion station, at a determinate distance therefrom, in which the continuous yarn is vulcanized in a direction of treatment. The plant also comprises a drawing unit, disposed downstream of the vulcanization station.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 120 to and is adivisional application of U.S. patent application Ser. No. 13/125,266,filed on Apr. 20, 2011, entitled “Plant for Making Continuous ElasticYarns Made of Silicone Material,” which claims priority to InternationalPatent Application No. PCT/IB2009/007164 filed on Oct. 20, 2009, thedisclosures of which are incorporated herein in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention concerns a plant for making continuous elasticyarns of silicone material usable in the medical field, that ofprotective technical fabrics and in those industrial fields for whichelastic yarns are required with a section of less than 0.7 mm,advantageously 0.3-0.4 mm, and even as little as 0.2-0.1 mm, resistantto certain chemical agents and/or to high or low temperatures, and inparticular cases usable as electric conductors. In particular, thepresent invention can be used to make so-called elastic yarns ofsilicone rubber.

The present invention also concerns the continuous elastic yarn obtainedusing the plant.

Here and hereafter in the description and claims, the term elastic yarnmeans generally a continuous extruded product, either filiform or with adifferent profile, for example packings, with a count higher than abead, filament, thread or profile, that is, the multi-filament type.

Description of Related Art

Plants are known, for the extrusion of silicone material used to makeextruded products of various section and thickness.

Known plants normally extend horizontally and comprise, in succession,feed means that feed the material in the form of paste, an extrusionstation, in which the extruded product is made, and a vulcanizationstation.

This type of known plant has the disadvantage that the extruded product,at the end of the extrusion process, is deposited on a conveyor belt orstrip that normally advances at a speed substantially equal to the speedof extrusion.

Since this feed occurs horizontally, or substantially horizontally, theextruded product being made is affected both by the extrusion pressureand also the force of gravity, under the action of which the extrudedproduct tends to modify its section, flattening before entering thevulcanization station, so that, at entrance to the vulcanizationstation, the extruded product no longer has the correct section but isdeformed, mainly due to the extrusion pressure.

This problem is accentuated when the extruded products to be made areparticularly fine, for example in the case of silicone based elasticyarns with a diameter of less than 0.7 millimeters, to as little as 0.2and 0.1 mm.

This problem also makes it very difficult to have a precise control onthe value of section obtained, and also it does not allow to guarantee auniform section over the length of the yarn.

Moreover, known plants do not allow to extrude materials such assilicone rubber, with a reduced section and in the liquid state, or atleast not totally solid, because the elastic yarn exiting from theextrusion station would not be firm enough to be deposited on a conveyorbelt or to be held by clamping means and drawn through the vulcanizationstation.

Another disadvantage of known plants is that the type of oven usuallyused in the vulcanization station are normally moved manually on eachoccasion, to be moved closer to or away from the vulcanization station,depending on the type of extruded product to be processed, but thisinterrupts the production process and increases both the economic costand the production times, and also does not guarantee precisionpositioning.

Known solutions for producing extruded products made of siliconematerial work on thicknesses having a slightly larger size than thosesought in the present invention, such as for example DE-C2-38 44 60.

Other solutions work on products in which the field of use is completelydifferent from the production of elastic yarns according to the presentpatent application, such as DE-A 1-101 45 945, which concerns theproduction of multi-layer optical cables, or W-A1-2008/074622, whichconcerns the production of windscreen wiper brushes, that is, withvalues of size and quality that cannot be compared with those requiredin continuous elastic yarns which are the object of the present patentapplication.

Purpose of the present invention is to achieve a plant for thecontinuous production of elastic yarns made of silicone material thatovercomes the shortcomings of the state of the art and allows to makeelastic yarns, simply and economically, with a section of much less than0.7 mm, advantageously less than 0.4 mm and even 0.2-0.1 mm.

The Applicant has devised, tested and embodied the present invention toovercome the shortcomings of the state of the art and to obtain theseand other purposes and advantages.

BRIEF SUMMARY OF THE INVENTION

The present invention is set forth and characterized in the independentclaims, while the dependent claims describe other characteristics of theinvention or variants to the main inventive idea.

In accordance with the above purpose, a plant for making continuouselastic yarns made of silicone material comprises at least an extrusionstation, a vulcanization station located downstream of the extrusionstation at a determinate adjustable distance therefrom, and at least adrawing unit, located downstream of the vulcanization station and ableto impart on the elastic yarn exiting from the extrusion station adrawing value in a ratio comprised between 2 and 6 (100-500%) beforevulcanization.

The extrusion station is provided with an extrusion body, in which thematerial is able to be introduced in an amorphous condition, andextrusion means, able to allow the material to exit from the extrusionstation along an extrusion axis, conditioning the shaping thereof.

The extrusion means are conformed so as to confer on the extrusion axisa substantially vertical direction, so that the elastic yarn exiting,disposed with a substantially vertical axis, is drawn due to the effectof the drawing unit, with the desired drawing ration and set accordingto at least the final thickness to be obtained, at least along theadjustable distance between the extrusion station and the vulcanizationstation.

The drawing action determines on the one hand the desired lengthening ofthe elastic yarn and thinning to the desired value of thickness, and onthe other hand the uniformity and regularity of its section; it alsoorients in a more regular manner the molecular chains inside the elasticyarn, allowing to obtain values of lengthening and force above thestandard of the base product.

The use of a drawing unit with a high drawing ration also allows toeliminate the deformation effect of the force of gravity that actsupstream of the vulcanization station, which in known solutions with atleast partly vertical extrusion, determines deformations andinaccuracies in the section.

Moreover, in particular in the case of very thin extruded products, itreduces the effect of the heat abatement caused by the introduction ofthe yarn inside the vulcanization oven, before the vulcanizationtreatment is completed.

In this way, continuous yarns of any length can be produced, and theyhave no surface imperfections, with constant technical-elasticcharacteristics for their whole length and with no deformation insection.

A plant according to the present invention can therefore be used to makeelastic yarns with controlled and uniform sections even much less than0.7 mm, as little as 0.4-0.3 mm and less.

Furthermore, since no horizontal movement is provided, it is alsopossible to introduce into the vulcanization station elastic yarns thatare still in a liquid, plastic or at least not solid state.

According to a variant, the plant provides a collection unit, locateddownstream of the vulcanization station, and able to collect the yarnexiting from the vulcanization station.

In another variant, the collection unit comprises said drawing unit sothat the elastic yarn, in the segment between the exit from theextrusion means and the entrance to the vulcanization station, reducesits section to the desired value while still keeping the regularity andquality of the section shape.

According to a variant, a plant according to the present inventioncomprises a controlled cooling station, located downstream of thevulcanization station and upstream of the drawing and possiblecollection unit.

The cooling station is able to cool the elastic yarn to a temperaturenear the environmental temperature, so as to prevent the finishedproduct from continuing the crystallization process also aftercollection and storage.

According to a variant, the vulcanization station comprises a zonalvulcanization oven, each zone being characterized by a heating system:high temperature, ultraviolet rays, microwaves or other.

According to another feature of the present invention, the vulcanizationstation is selectively movable in a vertical direction, and is heatadjustable according to the type of elastic yarn treated. This solutionallows to select the temperature of the various zones of thevulcanization oven with a simple programming of the plant, reducingmanpower and equipping times.

According to another variant, the cooling station is also selectivelymovable in a vertical direction and is heat adjustable according to thetype of extruded product treated.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

These and other characteristics of the present invention will becomeapparent from the following description of a preferential form ofembodiment, given as a non-restrictive example with reference to theattached drawing wherein:

FIG. 1 is a lateral schematic view of a plant for making elastic yarnsmade of silicone material according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the attached drawing, a plant 10 according to thepresent invention is used to make extruded products of siliconematerial, in this case continuous elastic yarns 30, with a thickness ofless than 0.7 mm, advantageously 0.3-0.4 mm, as little as 0.1 mm, ofsilicone rubber.

The plant 10 comprises feed means 11, an extrusion station 12, avulcanization station 16, a cooling station 17 and a drawing unit andcollection 26 of the yarn 30.

The feed means 11 feed the extrusion station 12 and are automatic.

In this case, the feed means 11 comprise a hopper 22, dosing pumps, ableto introduce into the hopper 22 the correct quantity of materialaccording to the capacity of the plant, and static and dynamic mixers,able to mix the material so as to prevent the formation of air bubbles.

The feed means 11 also provide a device able to keep the level ofmaterial inside the hopper 22 constant, so as to also keep constant theexit pressure of the material from the hopper 22.

According to a variant, in the case of material in the form of paste,the feed means 11 comprise a roller or a pair of rollers cooperatingwith each other, which feed the material in the form of a strip.

According to another variant, in the case of a continuous strip ofmaterial, the feed means 11 comprise a conveyor belt on which the stripis disposed.

The extrusion station 12 comprises an extrusion body 31 and extrusionmeans 15.

The extrusion body 31 is provided with compression means 13, dosingmeans 14 and a device 25 to distribute the material.

The compression means 13 compress the material and thrust it toward thedosing means 14. In this case, the compression means 13 comprise a wormscrew, sized according to the capacity of the plant 10, and a degassingzone, to eliminate the possible formation of air bubbles.

According to a variant, the compression means 13 provide a pistondevice.

The dosing means 14 are able to dose the material compressed by thecompression means 13 so as to feed the device 25 to distribute thematerial in a uniform and continuous manner.

In this case, the dosing means 14 comprise a dosing pump with gears anda plurality of pressure transducers, coordinated with the compressionmeans 13.

The transducers detect the pressure at entrance and at exit to/from thedosing means 14 and, according to this detection, send a signal to thecompression means 13 to regulate the speed of the material and to keep aconstant delivery through the dosing means 14.

The device 25 to distribute the material feeds the extrusion means 15uniformly. In this case, the extrusion body 31 has a vertical elbow-typeconformation. The material enters the extrusion body 31 in a horizontaldirection of feed, due to the effect of the pressure exerted by thecompression means 13, and exits from the extrusion means 15 along anaxis of extrusion D, with a substantially vertical direction, due to theeffect of said pressure and the force of gravity.

According to the conformation of the draw-plate, the yarn 30 obtained atexit from the extrusion means 15 can have a variable number of beads orfilaments, for example comprised between 2 and 30.

The draw-plate comprises corresponding perforations having a lead-in tofacilitate the entry of the material and a bevel at exit to facilitatethe detachment of the material.

According to a variant, the extrusion body 31 has a horizontalconformation.

According to a variant, the extrusion body 31 has a verticalconformation.

According to a variant, upstream of the draw-plate the extrusion means15 comprise at least a filter and at least a pre-drawing plate,advantageously two filters and two pre-drawing plates. This isparticularly advantageous to prevent obstruction of the perforations ofthe draw-plate and to distribute the material better, in the case wherethe extrusion means 15 include a draw-plate each, equipped with aplurality of perforations for the simultaneous production of acorresponding plurality of elastic yarns.

The presence of the filters upstream of the draw-plate is extremelyimportant so as to be able to break the memory effect that the extrusionscrew imparts to the material. The filters are chosen of a size such asto prevent the yarn, descending vertically, from twisting, knocking andfrom preventing the spinning.

The extrusion station 12 also comprises a heating and cooling device 24for the automatic heat-regulation of the various zones of the extrusionstation 12, so as to keep the ideal conditions of extrusion temperatureand pressure.

The elastic yarn 30 exiting from the draw-plate advances vertically,drawn by the drawing and collection 26 unit. In this case, thecollection unit 26 comprises drawing means 18, such as a motorizedroller, which exert a predetermined drawing force on the extrudedproduct 30 and guarantee that the extruded product 30 advances towardthe vulcanization station 16, maintaining a substantially verticaldirection, without horizontal displacements.

Furthermore, as a consequence of the drawing force of the drawing means18, the section of the continuous yarn 30 is reduced to the desiredsize, with a drawing factor that can vary, according to needs, from 2 to6, in this way reducing the section of the elastic yarn 30proportionally, yet keeping the quality and uniformity of the sectionshape high, and orienting the molecular chains in a more regular way.

The vulcanization station 16 comprises a zonal oven 27, each zone beingcharacterized by a heating system: high temperature, ultraviolet rays,or microwaves.

Inside the oven 27, the elastic yarn 30 is treated in a direction oftreatment “T”, substantially vertical and parallel to the axis of exit“D” of the yarn from the extrusion station 12.

The oven 27 is selectively movable vertically, with known mechanical orpneumatic devices, to be positioned at different distances “L” from thedraw-plate according to the type of elastic yarn 30 and the relativecrystallization and vulcanization times thereof.

In particular, the variation in the distance “L” between the exit fromthe extrusion station 15 and entry into the vulcanization oven 27 allowsto vary the drawing conditions on the continuous yarn 30 according tothe section to be obtained, both in the shape and thickness and also inorientation of the molecular chains, apart from, obviously the type ofyarn 30 itself.

In the case of continuous elastic yarns 30 according to the invention,the distance “L” typically varies between 400 and 1500 mm, in particularaccording to the final thickness of the elastic yarn 30 to be obtained.

The vulcanization oven 27 is heat-adjustable so as to vary thevulcanization temperature according to the type of elastic yarn 30treated.

The cooling station 17, located downstream of the vulcanization station16, is able to cool the elastic yarn 30 to a temperature near theenvironmental temperature so as to prevent the final product fromcontinuing the crystallization process after collection and storage.

The cooling station 17 is heat-regulated so as to guarantee that idealcooling temperature conditions are maintained, according to the type ofelastic yarn 30.

The collection unit also comprises, apart from the afore mentioneddrawing means 18, surface treatment means 19, control means 20 andcollection means 21, of a known type.

The surface treatment means 19 are able to treat the external surface ofthe extruded product 30 in order to confer upon it determinate physicalcharacteristics.

The control means 20 of the extruded product 30 comprise a rollerassociated with control devices and are able to control the physicalcharacteristics of the extruded product 30, such as the thickness,uniformity of section, elasticity and others.

The collection means 21 are able to collect and pack the elastic yarn 30for storage. The collection means 21 comprise an automatic reel-winderor a device to cut the elastic yarn 30 and insert it into containers.

It is clear, however, that modifications and/or additions of parts maybe made to the 10 as described heretofore, without departing from thefield and scope of the present invention.

The invention claimed is:
 1. A method for making continuous elasticyarns of silicone material, comprising at least an extrusion step,wherein by means of an extrusion station comprising an extrusion bodysaid material is made to exit along an extrusion axis, with aconditioned shaping, and at least a vulcanization station step carriedout in a vulcanization oven disposed downstream of said extrusion body,wherein: in said extrusion step, said extrusion means confer on theextrusion axis a substantially vertical direction, in a segment betweenan exit from the extrusion body and an entrance into the vulcanizationoven, that is variable between 400 and 1500 mm according to the finalthickness of the elastic yarn to be obtained, the elastic yarn issubjected to a drawing action performed by a drawing unit disposeddownstream of said vulcanization oven, in which a drawing ratioconferred on the elastic yarn before entering the vulcanization oven iscomprised in a value between 2 and 6 (100-500%), reducing the section ofthe elastic yarn proportionally, before the elastic yarn enters saidvulcanization oven, and in which the elastic yarn has a final thicknessof less than 0.7 mm and has a desired orientation of the molecularchains, and wherein the vulcanization oven is selectively moved withrespect to said extrusion station so as to vary said distance at leastaccording to a desired value of final thickness to be conferred on theelastic yarn.
 2. The method as in claim 1, wherein, in saidvulcanization station, said extruded product is vulcanized along aprocessing direction parallel or coincident to the extrusion axis. 3.The method as in claim 1, wherein a collection unit is provideddownstream of the vulcanization station to collect an extruded product,the collection unit comprising said drawing unit.
 4. The method as inclaim 1, further providing a controlled cooling of the yarn in a coolingstation located downstream of the vulcanization station and upstream ofthe collection unit.
 5. The method as in claim 1, further providing aheating and cooling step for heat regulation of the extrusion station.